Aiming at the small displacement of the valve core of thedirectly driven giant magnetostrictive highspeed onoff valve spool,a pistonslice hydraulic amplifier was designed.The Chienperturbation method and S.Way’s solution was used to establish the large deflection deformation model of the slice. Considering the influence of effectiveliquid bulk elastic modulus, a displacement inputoutput model of hydraulic amplifier is established. The simulation and experimental results show thatthe output displacement of the hydraulic amplifier is 0~470 μmwhen the amplifier input displacement is 0~51.1 μm, the magnification is more than 9 times, and the frequency response is about 150 Hz.